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In recent years, fluorescence imaging has become an indispensable tool for the exploration of biological processes, demonstrating both molecular specificity and high spatial and temporal resolution. Despite the significant progress made in this field, a number of challenges still exist which, if addressed could potentially result in the transformative development of fluorescent imaging for a plethora of biological applications. This may include the development of new fluorescent probes for the detection of unknown analytes, or the improvement of existing probes in order to enhance their properties. In this research, a fluorescent probe for the detection of hydrogen sulphide was repurposed for use as a ‘first of its kind’ fluorescent probe for the detection of hydroxylamine. In addition, the known peroxynitrite-mediated oxidation of boronic acid to phenol has been exploited for the development of a range of reaction based fluorescent probes. Initially non-fluorescent, each probe is ‘turned on’ in the presence of peroxynitrite, resulting in the formation of a highly fluorescent phenol derivatives. Such probes have been successfully evaluated during cell imaging experiments; demonstrating clear potential in the field of medical diagnostics. Specific applications may include ‘oxidative stress’, neurodegenerative disease and the evaluation of drug efficacy in the treatment of Alzheimer’s disease.

The synthesis and development of new materials and the improvement of the existing materials are a continuous quest for scientists. There is a constant need for new materials that have more advantages over the existing ones. The research to develop new materials can be appreciated in high magnitude, as the new materials improve the livelihood. In this dissertation, we are presenting our progress in developing new materials, such as fluorescence fluorophores as probes, and esterification catalysts. In the first part of the dissertation, the synthesis and characterization of a novel silicon analog of fluorescein (silyl fluorescein) was studied in detail. The photo-physical properties and toxicity studies of these fluorophores are also discussed. Compared to fluorescein, silyl fluorescein displayed a 90 nm longer wavelength in its absorption and emission. Silyl fluorescein showed good solubility in water and organic solvents, and has a considerable fluorescence quantum yield compared to fluorescein. Silyl fluorescein was found to be moderately toxic under light and non-toxic in dark, where as fluorescein toxicity was found to be greater than silyl fluorescein both in the dark and under light. Two probes from our novel silyl fluorescein fluorophore were developed and studied. SIF HySOx is probe for hypochlorous acid (HOCl), which is a reactive oxygen species (ROS) found in cells that are stressed due to various diseases. The HOCl probe was synthesized and its photo-physical properties were studied. It was found to be selective and sensitive only to HOCl. A fluoride probe (DTBDMS SIF P) was also developed from silyl fluorescein. Its synthesis and photo-physical properties were also studied. The probe displayed excellent selectivity and sensitivity to fluoride (TBAF) in the presence of other halides and bases. Future directions on novel fluorophore are briefly mentioned. Second part of the dissertation is focused on the screening of two organic esterification catalysts which were synthesized by Dr. Liu and Dr. Wong. The catalysts which are synthesized from pyridine and dinitrobenzene moieties were screened with several carboxylic acids and alcohols. Catalyst 8-4 was shown to be moderately active in the esterification of carboxylic acids and alcohols. It has no selectivity in the esterification of primary, secondary, tertiary alcohols, and the carboxylic acids that are attached to those carbons. Catalyst 9-1 however, was more efficient in the esterification of carboxylic acids and alcohols. Catalyst 9-1 displayed selectivity in the esterification of primary, over secondary, over tertiary alcohols, and the carboxylic acids that are attached to those carbons. Catalyst 9-1 gave up to 95% isolated yields.

The properties of the hyaluronan were investigated by using different fluorescence probes, because hyaluronan is a hopeful carrier of an active matter in medicine and cosmetics. Selected fluorescence probes were: cationic acridine orange, Nile Blue A, methylene blue, amphiphilic 4-Di-2-ASP and anionic fluorescein. Except from fluorescence and absorption spectra of the probes were observed electrostatic and hydrophobic interactions as well. The probes in solvents with different polarity (MeOH, EtOH, DMSO) showed the bathochromic shift in the emission maximum and quenching of the fluorescence with the increasing polarity of the solvents. The influence of the ionic strength on fluorescence properties of the probe acridine orange and 4-Di-2-ASP was investigated in aqueous solutions of chlorides. The formation of acridine orange dimer is inhibited with increasing ionic strength. CaCl2 increased the ionic strength the most, then prevented repulsion of carboxylate groups, so it means the expansion of hyaluronan cluster into the solution. However, the emission of the probe 4-Di-2-ASP was quenched with the addition of CaCl2 the most. The first additions of COO– groups cause the formation of dimers of AO shown as decreasing in extinction coefficient and fluorescence intensity. Next addition of the hyaluronan caused a depolymerization of formed dimers and the increase of the emission intensity. The repolymerization caused the decrease and then again the increase. In case of 4-Di-2-ASP was the pattern of the fluorescence (the intensity and the position of the emission) firstly the same, but at the concentration of 1 g dm-3 the emission intensity increased. The probes MB and F were used for spectroscopic studies of the interaction between methylene blue-fluorescein complex and anionic and cationic surfactants. The absorbance of separate MB and F changed only with the addition of surfactants with the opposite electric charge. Absorbance of the mixture MB-F changed with the addition of the CTAC surfactant, while the addition of SDS into the mixture caused only the change of MB absorption spectra.

This thesis is focused on investigation of phospholipid-hyaluronan system. First, appropriate method for preparation of bulk solution of phospholipid/lipid and suitable fluorescence probe were chosen. Sonification was selected as a method for preparation of bulk solution and pyrene was chosen as a fluorescence probe. From the group of phospholipids lecithin was selected. Next to phospholipid, lipid with no phosphate group (DPTAP) was utilized for comparison, alternatively a mixture of lipid (DPTAP) and phospholipid (DPPC). Instead of hyaluronan another polyelectrolytes (sodium polystyrene sulfonate, sodium alginate) were used too. Measurements were performed in water environment and in phosphate buffer saline (PBS). All investigation was accomplished by fluorescence spectroscopy and dynamic light scattering.